When any medium which has been heated to a temperature above that of the external environment is transported through pipes, there will inevitably be a loss of heat from the medium being transported, through the pipe wall and into the external environment. This heat loss is expressed in the amount of heat that will be lost in an applicable unit (W) times the length of pipe run (m). For the purposes of the calculation, the medium in the pipe is considered to be stationary. The result is a heat loss factor expressed in terms of energy lost per unit length of pipe (W/m).
The amount of heat lost to the outside environment is directly linked to the thermal characteristics of the material from which the pipe is manufactured. In general, metals exhibit high rates of thermal conductivity, whilst most plastics from which pipes are manufactured have relatively low rates of thermal conductivity. Because of this, plastic piping systems will transfer much smaller amounts of energy from the transported medium to the external environment, meaning that in plumbing terms, heated water will remain hotter when transported in plastic pipes than in metal pipes, and cold water is less likely to freeze in plastic pipes than in metal pipes when exposed to very low temperatures.
The thermal conductivity of Polybutene-1 (PB-1) is measured at 0.20 W/m2/°K, significantly better than many other thermoplastics of similar wall thickness. In terms of heat loss the following table applies:
|O.D. (mm)||I.D. (mm)||Thickness (mm)||Heat Loss (W/m2/oK)|
To obtain a measure of heat loss, divide the thermal conductivity factor (0.20) by the wall thickness in metres.
For example: 0.20 divided by 0.0016 = 125.0 for 18mm OD pipe above.
|1 metre||2 metres||3 metres||4 metres||5 metres||6 metres|
Polybutene-1 has a very low coefficient of thermal conductivity which, combined with its elasticity and flexibility, makes it ideal for the manufacture of plumbing pipes, especially those carrying cold water that may be exposed to freezing conditions.